1. FIELD OF THE INVENTION
This invention relates to sound absorbing panels for use in industrial sound control.
2. DESCRIPTION OF THE PRIOR ART
In recent years, industry has become increasingly aware of noise pollution, and, consequently, there has developed a need for sound control and sound absorption systems. The most common method used for sound control is thin, sound absorbing panels attached to the wall surface of the room where sound control is desired. Perhaps the latest design for a sound absorbing panel is the design shown in U.S. Pat. No. 3,858,676, which includes a perforated backing, a sound absorbing core, and a heavy textile front. While this design is suitable for attachment to a wall surface, it is unsuitable for use in those areas spaced apart from a wall surface where the sound absorbing panel must absorb sound from two opposing directions. Additionally, the use of a heavy textile material is expensive, difficult to assemble, and easily subject to damage.
Previous sound absorbing panel structures including that shown in U.S. Pat. No. 3,182,747, consisting of an open, microporous sound absorbing sheet adapted to be mounted at a predetermined distance from a wall. This panel structure required a wall for support, was difficult to construct, and was not adaptable to use in open spaces spaced apart from an existing wall.
In U.S. Pat. No. 2,968,327, a sound absorbing panel was illustrated consisting of a perforated, fibrous, acoustical material produced by mechanically delaminating the fibrous structure of the material in areas between the perforations to provide openings extending laterally from the perforations for air flow to reduce the air flow resistance of the material significantly and thereby enhance its sound absorption efficiency. This type of panel was difficult and costly to produce and also lacked the support necessary to span large vertical distances between the ceiling and floor of an existing room.
In U.S. Pat. No. 3,448,823, an acoustical panel was disclosed having a main sound attenuating body of integrated fibers and a fabric facing adhered thereto. The fabric was a woven glass fiber yarn, having nubs of glass fiber extending outwardly from the fabric. The use of glass fiber fabric was expensive, and the adhering of the fabric to the fibers also was difficult and expensive. On the other hand, U.S. Pat. No. 3,748,799 illustrated a sound absorbant panel wherein two smaller members were abutted end to end and enclosed in a channel-shaped, one piece edge member, but this design required the use of an expensive, and difficult to apply, double-faced adhesive tape along the edge of the panel. While this patent disclosed a facing material on the sound absorption material, the construction of the unit was too costly for wide spread use.
In U.S. Pat. No. 3,630,310, a sound absorbing fence was provided consisting of a solid upright backing panel on a framework and a layer of sound absorbing foam plastic material on the face of the plate directed toward the source of the noise by a screen of fabric, plastic, or metal practically transparent to the sound. This panel system, however, required a roof for protection, since the sound absorbant material was exposed to the elements and readily subject to damage thereby. In one other prior sound absorbing panel design, U.S. Pat. No. 3,253,947 disclosed a flexible sound attenuating material comprising a fabric face having, on at least one surface, a continuous elastomeric film containing randomly dispersed discrete particles of a high dense solid, such as lead. This panel system was very expensive due to the cost of the lead and could not use conventional, known sound absorbing materials for sound control. Additionally, the panels were easily subject to damage.
Even though there has been considerable activity in the design of sound absorbing panels, there has yet to be developed a sound absorbing panel which has a sound absorbing material completely protected from the elements. There has also not yet been provided an efficient sound absorbing panel which provides a method of preventing the sound absorbing material from being dispersed into the atmosphere, a condition normally occuring due to normal exposure of sound absorbing panels. Additionally, there has not yet been provided a sound absorbing panel which is highly successful in uses spaced apart from a wall or requiring sound absorption from opposing directions. In other words, none of the known prior systems are inexpensively adaptable to making a sound absorption wall spaced apart from an existing wall without first building a new wall. In addition to all the previous discussed, unsuccessful systems, there has yet to be provided a sound absorbing panel which is low cost and easy to assemble. The new and novel sound absorbing panels made possible by this invention provide the first known sound absorbing panels which can control sound from opposing directions, and which, additionally, shield the sound absorbing material from the elements while preventing the sound absorbing material from being dispersed into the working atmosphere.